Table 2 OpenMC EPR PWR full-core model: geometry, materials and simulation input.¹⁵.

Reactor / core layout

Simplified EPR PWR (OECD/NEA Monte Carlo Performance benchmark) with 241 17\(\times\)17 fuel assemblies. Square fuel-pin pitch 1.26 cm; assembly pitch 21.42 cm. Active core height 420 cm (\(z=\pm 210\) cm). Cylindrical radii (cm): core-lattice limit \(r=209\), inner/outer RPV \(r=229/249\); additional internal boundary at \(r=187.6\) (reflector interface). Axial planes: vessel bottom \(z=-250\), bottom nozzle \(-242\), bottom skirt \(-230\), active bottom \(-210\), core midplane 0, active top 210, top skirt 230, top nozzle 242, vessel top 250 (vacuum at \(\pm 250\)).

Fuel pins

UOX fuel, 4.95 wt% \(^{235}\)U, \(\rho =10.5\) g/cm\(^3\), \(T=900\) K; pellet radius \(r=0.4095\) cm. Zircaloy cladding, \(\rho =5.77\) g/cm\(^3\), \(T=613.15\) K; cladding outer radius \(r=0.475\) cm. Each 17\(\times\)17 assembly contains 265 fuel rods and 24 guide tubes; no instrument tube in this input. Guide-tube radii: \(r=0.56/0.62\) cm (inner/outer).

Coolant / moderator

Cold borated water (inlet): number density 0.07416 atom/b-cm, \(T=560\) K; Hot borated water (outlet): 0.06614 atom/b-cm, \(T=590\) K; both include B-10 and B-11 and S(\(\alpha ,\beta\)) for H in H\(_2\)O.

Reflectors / structures

Lower radial reflector (\(\rho =4.32\) g/cm\(^3\), \(T=560\) K), upper radial/top-plate region (\(\rho =4.28\) g/cm\(^3\), \(T=590\) K), bottom plate (\(\rho =7.184\) g/cm\(^3\), \(T=560\) K), bottom nozzle (\(\rho =2.53\) g/cm\(^3\), \(T=560\) K), top of fuel assemblies (\(\rho =3.044\) g/cm\(^3\), \(T=590\) K), top nozzle (\(\rho =1.746\) g/cm\(^3\), \(T=590\) K), reactor pressure-vessel steel (\(\rho =7.9\) g/cm\(^3\), \(T=575\) K).

Monte Carlo settings

Batches = 100, inactive = 50, particles/batch = 200,000; source: uniform box \([-160,-160,-183]\) to [160, 160, 183], only_fissionable=True.Temperature treatment: multipole=False (WMP disabled), method=’interpolation’, range 290–1500 K.

Nuclear data / depletion

ENDF/B-VII.1 HDF5 library; depletion chain chain_endfb71_12_pwr.xml for thermal spectrum; constant thermal power 4.59 GW\(_\text {th}\); Predictor integrator; time grid: 30 daily steps + 11 monthly steps (\(\approx\)1 year, 41 steps). Fuel volume set as \(265\!\times \!\pi r^2 h\) per assembly, scaled to 241 assemblies with \(r=0.4095\) cm, \(h=420\) cm.

Tallies / plots

Tallies disabled for production. XY mesh tally (100\(\times\)100) for flux and fission over the mid-plane; core spectrum tally with 500 log-spaced groups (1e-5 eV–20 MeV); material-colored geometry plots exported for QA.